1. Field of the Invention
The present invention relates to a vertical heat treatment apparatus for thermally treating a semiconductor wafer and, more particularly, to a method of improving a wafer transferring mechanism for transferring a semiconductor wafer between a carrier and a support ring type boat.
2. Description of the Related Art
Since a floor area of a vertical CVD apparatus is smaller than that of a horizontal CVD apparatus, a floor area of a clean room can be effectively used by employing the vertical CVD apparatus. The capacity of the clean room can be decreased, and dust in the room can be exhausted within a short time. Therefore, the vertical CVD apparatus is advantageous for maintaining high cleanness.
According to a vertical CVD apparatus, since a boat can be loaded in or unloaded to a reaction tube without contacting the inner wall of the reaction tube, an amount of dust is advantageously small. Since the vertical CVD apparatus has the above advantage, the vertical CVD apparatus is used for manufacturing not only a VLSI having a memory capacity of 1M bit but a VLSI having a memory capacity of 4M bit.
In recent years, as a semiconductor device is highly integrated, a circuit pattern of the device is three-dimensionally arranged in the thickness direction of the substrate. For this reason, in a manufacturing step of the semiconductor device, various thin films are formed on the substrate, and the thickness of each thin film tends to be decreased. Therefore, film thickness control during film formation must be more strict than conventional control, and film thickness uniformity on a wafer and between wafers must be improved.
Conventionally, when a thin film is formed on a semiconductor wafer W, the peripheral region of the wafer W is thinner than the central region thereof.
In a vertical CVD apparatus, therefore, a boat B having a support ring for supporting wafer is used. According to this, the wafer W is fitted in an inner step portion (concave portion) of the support ring, and the upper surface (pattern forming surface) of the wafer W has the same level as the upper surface of outer step portion of the support ring. A thick film portion is formed on the upper surface of the support ring to uniform the thickness of a pattern forming surface of the peripheral and central region of the wafer W.
However, when the above support ring type boat B is used, a wafer W cannot be automatically fitted in the inner step portion of the support ring. Conventionally, an operator manually sets the wafer W on the boat B. Since this manual setting is an inaccurate operation, an unexpected accident tends to occur. In addition, since a time for continuously opening a body cover is prolonged, an amount of dust entering in a process section is increased to contaminate the semiconductor wafer W, and to increase a rate of defective product.